1. Field of the Invention
The present invention relates to data communication on networks, and more particularly to a self-configuring data communication system and method.
2. Discussion of the Related Art
The popularity of small computers has brought into use a communication scheme wherein a number of stations timeshare a common communication medium, such as an electrically conductive cable. These stations may each compete with each other for access to the bus at overlapping time intervals. Therefore, some mechanism must be provided to prevent conflicting use.
U.S. Pat. No. 4,063,220 discloses a multipoint data communication system having multiple stations that may compete for a common bus on an asynchronous basis. Each station includes a circuit for detecting when its own transmission collides with the transmission of another station. Sources of inefficiency in the system disclosed in this U.S. patent include unproductive time during which signals from multiple stations are colliding, and unproductive time during which the bus is idle while stations are waiting to reattempt a transmission.
To alleviate the problem discussed above, it has been proposed that a communication system be implemented using multiple networks, with each station assigned to a single network. In such a multi-network system, the networks are connected together by a bridge circuit. As a result, any station is able to communicate with any other station, even when a sending station is assigned to a different network than a receiving station.
Each station assigned to a network has a unique system address. Data is communicated in units of "packets," with each packet containing the system address of the station sending the packet (the source system address) and the system address of the station which is to receive the packet (the destination system address). A bridge circuit is provided to detect a packet sent by a station on one network and forward the packet to another network (a nonsending network), at times when the packet has a destination address residing on the other network. In order to keep the traffic on each network to a minimum, the bridge circuit tends to forward only those messages having a destination corresponding to a station assigned to the nonsending network.
To minimize overall system traffic, stations should be assigned to networks such that most of the communication between stations occurs within a network, instead of between networks. In other words, stations should be assigned to a particular network such that most packets appear on only one network and are not forwarded by a bridge.
FIG. 1 is a diagram illustrating communication traffic between stations 1010-1170. In FIG. 1, continuous lines between two stations indicate relatively heavy traffic flow, while dotted lines indicate relatively light traffic flow. Stations not directly connected by a line do not directly send packets to each other.
Stations such as 1010, 1020, 1050, 1090, and 1110 are typically workstations or terminals. A station such as station 1060 is typically a station that communicates with a number of other stations and presents common resources to other stations, such as large volume data storage resources, e.g., disc devices.
As can be seen in FIG. 1, most stations have links primarily with one other station, which is typically a server station, such as stations 1060, 1070, or 1130. Most of the traffic is within a group of stations that talk to a particular server, but some traffic goes between groups.
FIGS. 2(A)-2(B) show a system configuration having station assignments that tend to isolate activity to one of networks 2001, 2002, or 2003. As can be seen in FIGS. 2(A)-2(B), the stations 1010-1170 are assigned to networks corresponding to the three groups shown in FIG. 1.
During typical operation of such a multi-network system, if traffic is found to be high on a certain network resulting in performance degradation, stations are manually reassigned to different networks. The task of manually reassigning is labor intensive and, therefore, costly for at least two reasons. First, it may be difficult to determine how stations should be reassigned in order to improve performance. Second, assuming that it is known how stations should be reassigned, reassignment may involve manually changing interconnection circuits with jumpers or switches. Interconnection circuits such as those encompassed by line 2400 typically reside in a patch panel within a satellite equipment room of an office floor. Manually changing interconnection circuits may take anywhere from minutes to several hours.